Field of the Invention
The present invention relates to a liquid ejection head and a liquid ejection device for ejecting liquid. More particularly, the present invention relates to a flow channel arrangement that can be used for liquid ejection heads realized by employing piezoelectric elements.
Description of the Related Art
Liquid ejection devices for recording images on recording mediums by ejecting liquid such as ink are generally equipped with a liquid ejection head for ejecting liquid. Liquid ejection heads realized by employing piezoelectric elements for the liquid ejection mechanism thereof are known. A liquid ejection head of this type is designed so as to expand/contract its pressure chambers by applying a voltage to the piezoelectric elements, which operate as components of the pressure chambers, in order to produce a pressure change in the pressure chambers. As a result of the pressure change, the liquid in each of the pressure chambers is ejected from the ejection port formed at an end of the pressure chamber. Known liquid ejection heads that include piezoelectric elements include so-called bend-mode liquid ejection heads. A bend-mode liquid ejection head includes plate-shaped piezoelectric bodies, each of which is sandwiched between a pair of electrodes and a diaphragm is rigidly secured to one of the electrodes. Liquid is ejected from the liquid ejection head by applying a voltage to the piezoelectric bodies between the related electrodes so as to expand/contract the piezoelectric bodies in a direction perpendicular to the direction in which the voltage is applied and thereby deforming the diaphragm in an out-of-plane direction (the thickness direction of the plate-shaped piezoelectric bodies). A bend-mode liquid ejection head can deform the diaphragms that form part of the walls of the pressure chambers only by applying a small voltage and hence requires only a low drive voltage.
So-called edge-shooters are known as a type of pressure chambers for forming liquid ejection heads. An edge-shooter has an ejection port formed at one of the longitudinal ends of a pressure chamber and liquid is ejected in a direction running in parallel with the longitudinal direction of the pressure chamber. Japanese Patent No. 5212627 discloses a liquid ejection head in which edge-shooter type pressure chambers are two-dimensionally arranged in planes that are perpendicular to the longitudinal direction of the pressure chambers. The liquid ejection performance of a liquid ejection head is improved by increasing the extent to which each of the pressure chambers of the head can change its volume as a result of deformation of the diaphragm related to pressure chamber. Since pressure chambers having a large length in the longitudinal direction thereof can be realized with ease in a liquid ejection head including edge-shooter type pressure chambers, it is possible for such a liquid ejection head to secure a large area for the plate-shaped diaphragms thereof so as to allow each of the pressure chambers to change its volume to a large extent. For this reason, pressure chambers can be two-dimensionally densely arranged in an edge-shooter type liquid ejection head without damaging the liquid ejection performance of the head.
There has been an increasing demand in recent years for recording apparatus for commercial applications such as print-on-demand type recording apparatus in response to the commercial demand that has also been observed in recent years for forming high resolution and high quality images. However, it is difficult for a liquid ejection head disclosed in Japanese Patent No. 5212627 to remove the air bubbles that have intruded into or otherwise appear in any of the pressure chambers thereof. When air bubbles stagnantly remain in a pressure chamber, the pressure change in the pressure chamber for ejecting liquid is absorbed by the air bubbles remaining there, so that a desired volume of ejected liquid and a desired liquid ejection velocity may not be achieved for the pressure chamber, and such a situation may end up with a serious problem that the pressure chamber can no longer eject liquid. If a pressure chamber cannot eject liquid for a certain period of time, the viscosity of the liquid located at and near the ejection port of the pressure chamber increases to give rise to a clogged ejection port there. Then, a problem of degraded ejection performance and defective ejection can take place.
In view of the above-identified problem, it is therefore the object of the present invention to provide a liquid ejection head including piezoelectric elements that can effectively remove the air bubbles in any of the pressure chambers thereof and suppress any possible increase of liquid viscosity at and near the ejection ports.